1. Field of the Invention
The present invention relates to a mobile telecommunication terminal device, a mobile telecommunication method, and a mobile telecommunication control program.
The present application claims priority of Japanese Patent Application No. 2004-232357 filed on Aug. 9, 2004, which is hereby incorporated by reference.
2. Description of the Related Art
For example, in the mobile telecommunication of a W-CDMA (Wideband-Code Division Multiplex Access) method, one frequency band is used in common by a plurality of users. That is, transmitting power for one frequency band to be supplied from a base station to a mobile unit is shared for use among a plurality of users.
As a result, if much power is consumed by one user, a limitation is imposed on an amount of power that can be assigned to other users and, therefore, the number of users (the number of mobile units) being able to carry out communication at one time is made to decrease.
On the other hand, signal receiving quality of the mobile unit changes depending on a positional relation and/or surrounding conditions and communication is made difficult due to poor signal receiving environments and additionally to decreased transmitting power to be fed from the base station.
Due to such communication environments as above, in order to simultaneously achieve uniformity of signal receiving quality of the mobile unit irrespective of its position and inhibition of occupation of transmitting power to be fed from the base station by only one user, the transmitting power from the base station is controlled from the mobile unit side.
In other words, if communication can be satisfactorily carried out even by a small amount of transmitting power, a request is made by the mobile unit asking the base station to decrease the transmitting power to be supplied to the mobile unit to enable many users to carry out communication at the same time, while, if a large amount of transmitting power is required for carrying out communication, the mobile unit makes a request asking the base station to increase the transmitting power to be fed to the mobile unit and, therefore, the mobile unit can maintain the receiving quality.
Here, the mobile unit detects an occurrence frequency (error rate) of a CRC (Cyclic Redundancy Check) error and, in order to keep the occurrence frequency at a level being not larger than a targeted low level (target error rate), controls transmitting power to be fed from the base station. That is, only when the error rate is raised until the error rate reaches the target error rate, a request is made by the mobile unit asking the base station to increase the transmitting power. The base station having received the request, if having sufficient transmitting power, increases the transmitting power to be fed to a corresponding mobile unit.
More specifically, the mobile unit detects the number of occurrences of CRC errors in received data in a unit time interval and changes a set value of a target SIR (Signal to Interference power Ratio) every time when the error rate reaches the target error rate due to the increased number of times of detection.
However, a conventional mobile telecommunication terminal device has a problem in that, even if an error rate is sporadically raised (in the case of a burst error) due to some reason (for example, a car hides momentarily behind a shadow of a building), the mobile unit recognizes that many errors have occurred and exerts control to increase transmitting power unnecessarily and, as a result, the number of users who can carry out communication in an area decreases.
FIGS. 3A and 3B are diagrams explaining problems of the conventional technology. FIG. 3A shows a change with time in the number of times of detection of CRC errors in a unit time interval in the mobile unit and FIG. 3B shows a change with time in set values of the target SIR (ordinate) on the mobile unit side.
As shown in FIG. 3A, every time the number of times of detection of CRC errors in a unit time interval becomes large and every time an error rate reaches the target error rate (FIG. 3A), the mobile unit changes a set value of the target SIR (target SIR) (FIG. 3B) so as to have a large value.
Moreover, when a burst error occurs, in particular, that is, when the number of times of detection of CRC errors becomes extremely larger in a unit time interval, the set value of the target SIR also is set to become extremely larger.
As a result, transmitting power to be fed to the corresponding mobile unit is changed to have an extremely large value and the number of users who can carry out communication in the area becomes extremely small.
Moreover, since a change of a set value of the target SIR is made only in every unit time interval, if the target SIR is once set to be a large value, it is not easy for the target SIR to converge on a standard target SIR value.
Due to this, a state in which transmitting power to be supplied from the base station to the corresponding mobile unit continues long and, during the period, the number of users being able to carry out communication is limited.